1. Field of the Invention
The present invention relates generally to differential gear mechanisms of the side gear type and more specifically to those including means for locking up the differential upon the occurrence of a predetermined degree of differentiation, and to the construction of transfer cases for four wheel drive vehicles utilizing such differential gear mechanisms.
2. Description of the Prior Art
Differential gear mechanisms of the side gear type are well known in the art. See, for example, U.S. Pat. No. 2,932,218 (Russell). They have generally included a pair of side gears and one or more pinion gears carried for rotation in a housing to which bearing means are fixed for supporting the pinions.
Also well known in the prior art is the use of side gear type differentials in four wheel drive transfer cases and the provision of means for detecting the occurrence of a predetermined amount of differentiation and thereupon preventing further differential action. Examples of these features may be seen in U.S. Pat. No. 3,811,341 of applicant. Although these prior art locking differentials have been generally satisfactory, certain disadvantages have been noted.
First, the capacity of clutches used in the lock up mechanisms must be relatively high since they carry the load between the input and one of the outputs.
Further, the means employed to sense the occurrence of differentiation in prior art devices have been found to be critically sensitive to variations in tolerances, friction forces, and inertias of moving parts.
Still further, the necessity of providing a separate pinion housing and separate pinion bearing structure makes these differential gear mechanisms a relatively expensive element in vehicle drive lines.
Still further, the prior art locking differentials, when employed in a transfer case environment, are long when measured along the axis of the drive line since the side gears in this environment are spaced axially along the drive line axis and the front axle power take off member is disposed outboard of the associated side gear.